[es6] stage harmony_rest_parameters

BUG=v8:2159
R=arv@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/1099813005

Cr-Commit-Position: refs/heads/master@{#27978}

src/flag-definitions.h

@@ -191,12 +191,12 @@ DEFINE_IMPLICATION(es_staging, harmony)
   V(harmony_proxies, "harmony proxies")                         \
   V(harmony_sloppy, "harmony features in sloppy mode")          \
   V(harmony_unicode_regexps, "harmony unicode regexps")         \
-  V(harmony_rest_parameters, "harmony rest parameters")         \
   V(harmony_reflect, "harmony Reflect API")                     \
   V(harmony_spreadcalls, "harmony spread-calls")
 
 // Features that are complete (but still behind --harmony/es-staging flag).
 #define HARMONY_STAGED(V)                               \
+  V(harmony_rest_parameters, "harmony rest parameters") \
   V(harmony_unicode, "harmony unicode escapes")
 
 // Features that are shipping (turned on by default, but internal flag remains).